nixos/tests/containers.nix: Don't ping

This randomly fails with "Destination Host Unreachable". That
shouldn't happen, since all interfaces/routes should be up after
"nixos-container start" returns. Need more investigation...

(cherry picked from commit 19fc92a8ed7a63ba4e296941ac804298f936d792)
postgresql: Update to 9.0.18, 9.1.14, 9.2.9, 9.3.5

(cherry picked from commit e4e5502966636e1752005664c04baa06d13965a1)
Remove Subversion from the installation CD

(cherry picked from commit 5e96158234d93e624f179cf47e1e261670c1f901)
Shut up a warning in stage 2

(cherry picked from commit 39a67503621307692c00ec91edf8cdd3b0c23da2)